Electric current carrying element



Patented Oct. 27, 1936 'ELECTRIO CURRENT CARRYING ELEMENT Franz R.Hensel, Indianapolis, Ind., asslgnor, by mesne assignments, to P. R.Mallory a Co. Inc., Indianapolis, Ind., a corporation of Delaware NoDrawing. Application June 25, 1935,

Serial No. 28,303

'5 Claims. (Cl. 219-4) This invention relates to electrical contactingelements and the like such as welding electrodes and'electrical contactsgenerally.

The present application comprises a continu- 5 ation in part of mycopending application, Serial Number 6,857, filed Febmary'16, 1935.

An object of the invention is to improve the strength, hardness andtemperature-resistant properties of contacting elements of the typedisclosed.

Another object is to improve the electrical characteristics ofsuch-elements, including their conductivity and arc-snuflingproperties.

Further objects are to prevent oxidation of the contacting elements bothduring and after formation thereof. A specific object is to producecontacting elements, such as welding electrodes, contacts, trolley shoesand wheels, and contactors generally.

Other objects of the invention will be apparent from the followingdescription taken in connection with the appended claims.

Alloys of copper and zinc in various proportions have been made and usedcommercially for many years.' These alloys, in the cast form, are quitesoft and can only be hardened to a very limited extent by cold working.Furthermore, the increased hardnem can only be retained at fairly lowtemperatures. If these alloys are heated very substantially the hardnessis 10st and can only be regained by further cold working.

Copper-chromium alloys, on the other hand, while having many desirableproperties, oifer difiiculties in casting and working, have a. marked 5tendency to. deteriorate through oxidation during and after casting andworking, have a tendency to excessive grain growth during treatment andare quite susceptible to arcing when used for some electrical purposes,such as for welding electrodes.

The present invention comprises the combination of elements, methods ofmanufacture, and

- the product thereof brought out and exemplified in the disclosurehereinafter set forth, the scope of the invention being indicated in theappended claims.

While a preferred embodiment of the invention is described herein, it iscontemplated that considerable variation may be made in the method ofprocedure and the combination of elements without departing from thespirit of the invention.

The invention contemplates the provision of a contacting element formedof an alloy of copper, chromium and zinc. This alloy, as will beapparlii ent from the following description, possesses a number ofdesired characteristics for such purposes not found in the binary alloysof copper and chromium or copper and zinc in addition to most of thedesirable characteristics of these binary alloys.

The completed copper-chromium-zinc contacting element, to have the mostdesirable characteristics should contain the component ingredients inthe following ranges of proportions:

Zinc 0.1 to 5.0% 1

Chro i 0.1 to 2.5% Copper Remainder The preferred alloy for mostcontactors, including welding electrodes, has a composition, when 15completed, approximately as follows:

Zim-

Chrnminm 0.5% Coppern, Remainder Another suitable alloy for contactingelements 20 has the composition:

Zine 0.75% Chromium 1.50% Copper--....,-. Remainder 26 This alloy maysometimes be used as the final composition or it may be diluted with anequal proportion of copper resulting in a final .alloy of the followingapproximate composition:

Zinc 0.3% Chrom 0.5% Copper Remainder It will be noted that some of thezinc and chro- 35 mium are lost in remelting due to oxidation andvolatilization.

zinc in the finished alloy, for example, it is necessary to introduce0.55% to 0.65% of zinc into the original melt. About half of the excesszinc 50 is consumed as a deoxidizer, the zinc being converted to zincoxide and separating as a slag. The rest of the excess is volatilizeddue to the low boiling point of the -zinc. This volatilized zinc, whenit comes into contact with the air, at a s the crucible in the form of awhite smoke.

In the further treatment of the alloy after solidification it may befirst heated to a temperature of 600 C. to 1050 C.,' and preferablyabove 700 C. for a short time, such as from 10 to 30 minutes. After themetal has reached the desired temperature it may be cooled quickly fromthe high temperature (quenched). The next step is preferably to heattreat the quenched alloy at a temperature of 350 C. to 600 C. for aperiod of from 10 minutes to 30 hours, depending on the temperature, thepercentage of hardener used, and the results desired.

The alloy may then be cold worked to obtain a cold reduction ofapproximately 20% and further cold reduction, up to 50% or more, maybeapplied to further increase the hardness. It has been found that theconductivity will not be appreciably decreased by these furtherreductions.

For a maximum hardness and conductivity, however, it is preferable toapply a series of cold reductions alternated with relatively lowtemperature heat treatment, preferably within the range 400 C. to 500 C.The number of cold workings with intermediate heat treatments may varywith the properties desired inthe finished product.

Instead of the cold working; the alloys may be hot forged according tousual methods and it will be found that the resulting hot-forged productwill also have a hardness greater than the alloys of the prior artpreviously mentioned.

Alloys having the above mentioned proportions of zinc 0.3% and chromium0.5% have been obtained after heat treatment with an electricalconductivity of 79.85% of that of pure forged copper and a Brinnellhardness'of 130. Such high conductivity in an alloy ofsuch high hardnessis very desirable for many of the applications mentioned and has beendifiicult to obtain in the past.

Another alloy containing 1.50% zinc, 030%-v The heat-resistantproperties of the present alloy are likewise greatly improved, thehardness and electrical conductivity being maintained indefinitely attemperatures in the order of 400 C. to 475 G.

Since the zinc acts as a strong deoxidizer it is not necessary to addother deoxidizers commonly used, such as silicon, aluminum or magnesium,for this purpose.

The presence of the zinc likewise tends to pre-- vent excessive surfaceoxidation in the finished, solidified alloy and is particularlyadvantageous where they are heated to high temperatures. The surfaceoxidation in copper-chromium alloys is quite serious since the oxygenpenetrates along the grain boundaries and tends to make the alloybrittle. In the present alloy, the chromium is protected by the zinc.which will oxidize in preference to the chromium.

As is well known, zinc added to pure copper tends to decrease itsconductivity quite considerably. It is surprising, therefore, to findthat alloys of copper, chromium and zinc exhibit com paratively highelectrical conductivity in the cat with the addition of and heat treatedstate. 0.5% or less of zinc the conductivity is not re ducedbelow to andwith even 1.5%

zinc the conductivity is found to be at least 65% that of copper whenthe alloy is in the cast, heat treated condition.

The alloy likewise has improved arc-snufling properties, due to thepresence of the zinc. This is highly advantageous for the electricalapplications, such as in the use of the alloy for pressure weldingelectrodes and as a contact material. The low-boiling zinc (930 0.)tends to produce a gaseous phase which extinguishes the arc. Thesearcing characteristics are improved by increasing the proportions ofzinc.

This alloy is further characterized by small grain size. Copper-chromiummaterials must be heated to above 900 C. before quenching in water. Thatelevated temperature, however, is normally very conducive to graingrowth, the size of the grains usually depending on the length of timethe material is held at the elevated temperature. With the presentalloy, containing zinc, the grain size appears to be considerablyreduced from that found in other copper-chromium alloys.

In the present alloy the proportions of zinc are kept below 5% andaccordingly no low-melting point phase is formed, such as that formed inalloyscontaining zinc in high proportions. This allows a wider range offorging or hot working temperatures and presents a decided improve-.

carried out in specific embodiments thereof, it is' not desired to belimited thereby .but it is intended to cover the invention broadlywithin the spirit and scope of the appended claims.

What is claimed is:

1. A welding electrode composed of 0.1 to 5.0% zinc, 0.1 to 2.5%chromium and the remainder copper.

2. A welding electrode containing about 0.1 to 5.0% zinc,- 0.1 to 2.5%chromium and the remainder substantially all copper, characterized bythe combination of high hardness and high electrical conductivity.

3. An electric current carrying member containing about 0.1 to 5.0%zinc, 0.1 to 2.5% chromium and the remainder substantially all copper,characterized by a combination of high hardness and high electricalconductivity, and further characterized by the ability to maintain itshardness and high conductivity at temperatures in the order of 400 C.

4. An electric current carrying member containing about 0.1 to 0.75%zinc, 0.1 to 2.5%

chromium and the remainder substantially all copper, characterized by acombination of high

